In case you have not seen it yet, the forum has a whole section for sprinter based class C vans.
https://sprinter-source.com/forum/forumdisplay.php?f=57
LTV and Winnebago are probably the most discussed, but there is more in common in that platform than difference, so it is worth looking over what people have done on them.
I am not sure why it didn't occur to me earlier that you were referring to a class C RV built on a sprinter chassis rather than a class B that uses the conventional sprinter body.
There isn't any reason that you cannot do a solar install yourself. It might even be possible to get more power up there. If you measure carefully, it might even be possible to get 50% more solar power than the 400 watts using more conventional RV size panels (nominal 27 x 58 inch). I have not attempt this yet, but I have done some class A RVs.
Just to rough out some costs though:
- 4 panels x 180 watt = est $1000
- Mounting hardware for 4 panels = est $500
- Charge controller capable of handling 4 x 180 watt panels into a 12 volt system = something similar to a midnight classic 150 S = est $550
- Wires, connectors and cable management =est $300
Usually there are not any rails on these roofs, so the attachment is a combination of VHB tape and expansion bolts.
Some people will run the PV wires down behind the refrigerator.